The present invention pertains to systems and methods for passivating the copper seed layer deposited in Damascene integrated circuit manufacturing. More specifically, the invention pertains to systems and methods for depositing the copper seed layer by physical vapor deposition, while passivating the copper during or immediately after the deposition in order to prevent excessive oxidation of the copper. The invention is applicable to dual Damascene processing.
Integrated circuit (IC) manufacturers have traditionally used aluminum and aluminum alloys, among other metals, as the conductive metal for integrated circuits. While copper has a greater conductivity than aluminum, it has not been used because of certain challenges it presents, including the fact that it readily diffuses into silicon oxide and degrades insulating electrical properties at very low doping concentrations. Recently, however, IC manufacturers have been turning to copper because of its high conductivity and electromigration resistance, among other desirable properties. Most notable among the IC metalization processes that use copper is Damascene processing.
Damascene processing is a method for forming metal lines on integrated circuits. It involves formation of inlaid metal lines in trenches and vias formed in a dielectric layer (inter-metal dielectric). A barrier layer that blocks diffusion of copper atoms is typically formed over the dielectric layer and underneath the metalization. Damascene processing is often a preferred method because it requires fewer processing steps than other methods and offers a higher yield. It is also particularly well-suited to metals such as Cu that cannot readily be patterned by plasma etching.
In a typical copper IC process, the formation of the desired conductive wires on the chip generally begins with a seed layer, usually deposited by physical vapor deposition (PVD). The seed layer provides a conformal, conductive layer on which a thicker layer of copper is electrofilled in order to fill in the features (e.g., trenches and vias) of the semiconductor wafer. One problem with the use of copper as the conductive metal is that it does not self-passivate, that is, it readily turns into copper oxide when exposed to oxygen. Unlike aluminum oxide, copper oxide does not protect the underlying metal. Rather it allows copper to continue to react until all the copper is converted to copper oxide. In Damascene processing, this can occur if the wafer is exposed to atmosphere, or if it is exposed to oxygen plasma during etch. It is a particularly acute problem when seed layers are involved. Copper seed layers are very thin, typically on the order of 1500 xc3x85 and as little as 50 xc3x85 on the bottoms and sidewalls of vias and trenches, and are therefore rapidly consumed.
What is needed therefore is a technique for protecting copper seed layers from oxidation.
The present invention pertains to systems and methods for passivating the copper seed layer deposited in Damascene integrated circuit manufacturing. More specifically, the invention pertains to systems and methods for depositing the copper seed layer by physical vapor deposition, while passivating the copper during or immediately after the deposition in order to prevent excessive oxidation of the copper. The invention is applicable to dual Damascene processing.
One aspect of the invention provides for a method for passivating a copper seed layer on an integrated circuit substrate. The copper is deposited by physical vapor deposition. The method incorporates nitrogen to form a passivating layer on the surface of the copper seed layer. The method may employ a hollow-cathode magnetron to deposit the copper. Regardless of the reactor chosen, the method preferentially employs a nitrogen gas or plasma. A separate annealing operation may or may not be carried out on the copper seed layer. The nitrogen can be introduced after PVD deposition in a separate reactor. The passivating layer may be pure Cu3N. The method may be used in Damascene processing and dual Damascene processing. The method may also include controlled oxidation of the copper seed layer. This may be carried out before a copper fill or copper plating operation. The controlled oxidation may form 20-100 xc3x85 of copper oxide.
Another aspect of the invention provides for a method for passivating a copper seed layer on an integrated circuit substrate. The copper is deposited by physical vapor deposition. The method incorporates hydrogen to form a passivating layer on the surface of the copper seed layer. The method may employ a hollow-cathode magnetron to deposit the copper. Regardless of the reactor chosen, the method preferentially employs a hydrogen gas or plasma. No separate annealing operation need be carried out on the copper seed layer. The hydrogen can be introduced after PVD deposition in the same reactor or a separate reactor. The method may be used in Damascene processing and dual Damascene processing. The method may also include controlled oxidation of the copper seed layer. This may be carried out before a copper fill or copper plating operation. The controlled oxidation may form 20-100 xc3x85 of copper oxide.
Another aspect of the invention provides for a method for passivating a copper seed layer on an integrated circuit substrate. The copper is deposited by physical vapor deposition. The method incorporates a passivating agent to form a passivating layer on the surface of the copper seed layer. The passivating agent is chosen from the group comprising: F2, CF4, Cl2, SiH4 and Ge. The method may employ a hollow-cathode magnetron to deposit the copper. No separate annealing operation need be carried out on the copper seed layer. The passivating agent can be introduced after PVD deposition in a separate reactor. The method may be used in Damascene processing and dual Damascene processing. The method may also include controlled oxidation of the copper seed layer. This may be carried out before a copper fill or copper plating operation. The controlled oxidation may form 20-100 xc3x85 of copper oxide.
Another aspect of the invention provides for an apparatus module for physical vapor deposition of copper seed layer on an integrated circuit substrate in order to form a passivating layer on top of the copper seed layer, including a PVD chamber, a hollow-cathode magnetron, a copper target, a source of a neutral sputtering gas and a source of a passivating agent. The passivating agent may be nitrogen or hydrogen, or may be chosen from the group comprising: F2, CF4, Cl2, SiH4 and Ge. The apparatus is used to form part or all of a copper layer seed in a manner that passivates the copper. The apparatus may be used in Damascene or dual Damascene processing.